1. Field of the Invention
The present invention relates to a so-called plate fin heat exchanger which is internally provided with fin plates.
2. Description of the Related Art
As the plate fin heat exchanger (hereinafter also simply referred to as “heat exchanger”), the one described in Japanese Patent Application Laid-Open No. 7-167580 is conventionally known. This heat exchanger includes a heat exchange part including plural flow passages for carrying first fluid and flow passages for carrying second fluid alternately arranged within a casing. Concretely, as shown in FIGS. 4A and 4B, a heat exchange part 100 includes a plurality of partition plates 102 placed in parallel at intervals; corrugated plate-like fin plates 104 each of which is placed between the partition plates 102; and sealing members 106 placed on both sides of the fin plates 104 in their width direction so as to sandwich them, the sealing members 106 sealing the space between the partition plates 102 along the fin plate 104 to form a flow passage r together with the partition plates 102 therein. In order to transfer the heat of a fluid flowing in the flow passage r with the fin plate 104 placed therein to a pair of partition plates 102 with the fin plate 104 therebetween, the plate fin 104 connects the pair of partition plates 102 at specific positions arranged at intervals between one sealing member 106 and the other sealing member 106 (refer to FIG. 4B). In the thus-constituted heat exchange part 100, a number of flow passages r are arranged in layers.
In this heat exchanger, each of two kinds of fluids (e.g., high-temperature fluid and low-temperature fluid) are alternately flowed in each of plural layers of flow passages r arranged in the heat exchange part 100 in order to perform heat exchange between the two kinds of fluids flowing in adjacent flow passages through the partition plate 102. At that time, the fin plate 104 transfers the heat of the fluid flowing between the pair of partition plates 102 with the fin plate 104 therebetween to the pair of partition plates 102, whereby the efficiency of the heat exchange is improved. The thus-constituted heat exchanger is used as heat exchangers for various purposes such as an air separator which requires compactness since it has a relatively simple structure and a high overall heat transfer coefficient.
Protection parts 110 each provided with an internal space r1 are generally disposed on both outsides of the above-mentioned heat exchange part 100 respectively in the arrangement direction of the flow passages r of the heat exchange part 100 (in the vertical direction in FIG. 4B). The protection part 110 is a member provided to protect the flow passage r for carrying the fluid from damage attributed to a contact of the heat exchange part 100 with other members, etc. at the time of the installation or transfer, etc. of the heat exchanger. Namely, even if the heat exchange part 100 is contacted with other members and the outer surface of the heat exchange part 100 dents, the dent occurs only within the range of the protection part 110, and therefore the deformation resulting from the dent is not generated on the partition plates 102 constituting the flow passages r, etc. which are inside the protection part 110. The protection part 110 has the same structure as each flow passage r of the heat exchange part 100.
In the above-mentioned heat exchange part 100, since the sealing member 106 generally has higher rigidity than the fin plate 104, and the fin plate 104 generally has more excellent heat transfer performance than the sealing member 106, the following property to thermal change is higher in the fin plate 104 than in the sealing member 106. Therefore, if the temperature of the fluid flowing in each flow passage r in the heat exchange part 100 suddenly changes, the fin plate 104 deforms more largely than the sealing member 106 in each flow passage r based on this temperature change. Such a difference in the temperature change-based deformation amount between the sealing member 106 and the fin plate 104 causes a stress (thermal stress) based on this difference in deformation amount in a specific site of the heat exchange part 100. Concretely, although the sealing member 106 does not expand so much by a sudden temperature change of the fluid (e.g., 50° C./min, etc.), the fin plate 104 is apt to expand more largely than the sealing member 106. At that time, as shown in FIG. 5, although the space between a pair of partition plates 102 with the flow passage r therebetween is not changed largely in the vicinity of a site where the highly rigid sealing member 106 is disposed, the space is expanded by the expansion of the fin plate 104 in a site distant from the sealing member 106 or in the width-directional center site of the flow passage r. Such deformation of the partition plates 102 causes the deformation-attributed stress (thermal stress) in a specific site of the partition plates 102. This thermal stress generally generates, upon a sudden change in flow rate or temperature in the heat exchange part 100, due to the difference in the deformation amount based on the change in temperature or the like of each member, and such thermal stress attributed to the difference in deformation amount of each member is similarly caused in the specific site not only by the change in temperature or the like of the high-temperature fluid but also by the change in temperature or the like of the low-temperature fluid.
In general, since a number of (e.g., several hundreds) flow passages r are arranged in layers in the heat exchange part 100, the deformation amount from the initial position of the partition plate 102 separating the flow passages r from each other is increased from the center toward the outer side (the upper side and lower side in FIG. 5) in the arrangement direction of the flow passages r. This is attributed to that the deformation amount in each layer (each flow passage) is added from the center toward the outer side as shown in FIG. 5.
Therefore, as in the case where the heat exchanger is used in a chemical plant, for example, the deformation is repeated at each time of sudden change in temperature of the fluid performing the heat exchange or start-stop during the entire period of use, and as a result, the fatigue based on the thermal stress is accumulated most in a specific position of the partition plate 102 which receives the largest deformation amount and separates the protection part 110 from the flow passage r on the inside of the protection part 110, whereby the probability of damage such as hole or cracking in the partition plate 102 becomes high.
If damage such as hole occurs in the partition plate 102 at this position, the fluid flowing in the flow passage r flows into the internal space r1 of the protection part 110. Since the fluid in high-pressure state flows in the flow passage r of the heat exchange part 100 in operation, continuous outflow of the fluid from the flow passage r into the internal space r1 of the protection part 110 can lead to leak of the fluid from the internal space r1 of the protection part 110 to the outside of the heat exchanger due to the gradual increase of pressure within the protection part 110.
Thus, for preventing such leak of the fluid out of the heat exchanger, it has been considered to enhance the rigidity of the fin plate 104 or to suppress the deformation amount of the partition plate 102 between the flow passages r by inserting a reinforcing member into each of the flow passages r to suppress the deformation amount of the partition plate 102 and thereby the accumulation of fatigue.
However, when the rigidity of the fin plate 104 is enhanced in this way, the heat conductivity of the fin plate 104 is reduced, whereby the heat exchange efficiency of the heat exchange part 100 is deteriorated, resulting in deterioration of performance of the heat exchanger. The use of the reinforcing member involves a problem such as increase in size or weight of the device.